1-Open it before you open the game.
2- Set the Water Level and Wave level and Press "Set"
3- Open the game.
(NOTE: no need to start a new game)
4- Enjoy the swiming

(NOTE*2:Dont set the water too high or your screen will turn black)
(NOTE*3:The water level will always be the one you setted, to return to default press the "Default" key)
(NOTE*4:You can't set the water level while In-Game)